DESCRIPTION:
Mount Shasta and Vicinity, California

Shasta84_mount_shasta_with_shastina_1984.jpg
Mount Shasta and Shastina, California.
USGS Photograph taken by Lyn Topinka, 1984
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Mount Shasta

Location: Siskiyou County, California

Latitude: 41.40 North

Longitude: 122.18 West

Height: 4,317 Meters (14,161 Feet)

Type: Stratovolcano

Composition: Silicic andesite to dacite

Eruptive History:

Initiation of activity: 0.59 million years ago

Cone collapse and avalanche: 300,000 years ago

Sargents Ridge Cone: less than 250,000 years ago

Misery Hill Cone: less than 130,000 years ago

Shastina Cone: around 9,500 years ago

Hotlum Cone: less than 9,500 years ago

10 or more additional Holocene eruptions

Mount Shasta has erupted, on the average, at least once per 800 years during the last 10,000 years, and about once per 600 years during the last 4,500 years. The last known eruption occurred about 200 radiocarbon years ago. Eruptions during the last 10,000 years produced lava flows and domes on and around the flanks of Mount Shasta, and pyroclastic flows from summit and flank vents extended as far as 20 kilometers from the summit. Most of these eruptions also produced alrge mudflows, many of which reached more than several tens of kilometers from Mount Shasta. Future eruptions like those of the past could endanger the communities of Weed, Mount Shasta, McCloud, and Dunsmuir, located at or near the base of Mount Shasta. Such eruptions will most likely produce deposits of lithic ash, lava flows, domes, and pyroclastic flows. Lava flows and pyroclastic flows may affect low- and flat-lying ground almost anywhere within about 20 kilometers of the summit of Mount Shasta, and mudflows may cover valley floors and other low areas as much as several tens of kilometers from the volcano. On the basis of its past behavior, Mount Shasta is not likely to erupt large volumes of pumiceous ash in the future; areas subject to the greatest risk from air-fall tephra are located mainly east and within about 50 kilometers of the summit of the volcano. The degree of risk from air-fall tephra decreases progressively as the distance from the volcano increases.

Mount Shasta is located in the Cascade Range in northern California about 65 kilometers (40 miles) south of the Oregon-California border and about midway between the Pacific Coast and the Nevada border. One of the largest and highest of the Cascade volcanoes, snowclad Mount Shasta is near the southern end of the range that terminates near Lassen Peak. Mount Shasta is a massive compound stratovolcano composed of overlapping cones centered at four or more main vents; it was constructed during a period of more than 100,000 years. Each of the cone-building periods produced pyroxene-andesite lava flows, block-and-ash flows, and mudflows originating mainly at the central vents. Construction of each cone was followed by eruption of domes and pyroclastic flows of more silicic rock at central vents, and of domes, cinder cones, and lava flows at vents on the flanks of the cones.

Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13 kilometers (8 miles) west of Mount Shasta. Evidence of geologically recent eruptions at these two main vents and at flank vents forms the chief basis for assessing the most likely kinds of future eruptive activity and associated potential hazards.

Peter Skene Ogden was a chief trader with the Hudson's Bay Company. In the period 1824-1829, he led five trapping expeditions to the "Snake Country" -- the upper reaches of the Columbia. ...

"Tuesday 14th. (February 14, 1827) Wind blew a gale. If the ship destined for the Columbia be on the coast in this stormy weather, I should feel anxious for her. Having 40 beaver to skin and dress I did not raise camp. It is a pleasure to observe the ladys of the camp vieing who will produce on their return to Ft. Vancouver the cleanest and best dressed beaver. One of the trappers yesterday saw a domestic cat gone wild. It must have come from the coast. All the Indians persist in saying they know nothing of the sea. I have named this river Sastise River. There is a mountain equal in height to Mount Hood or Vancouver, I have named Mt. Sastise. I have given these names from the tribes of Indians."

According to legend, about 1821, a Spanish explorer reported that while climbing Mount Diablo near San Francisco he saw Mount Shasta. He called it "Jesus and Maria" because of the double peaks. About this time the Russians probably viewed Mount Shasta from the coast near Fort Ross. Hudson Bay Company trapper, Peter Skene Ogden left Fort Vancouver and journeyed through central Oregon, trapping beaver. The trappers wanted fur from beaver, otter, and martins to export to England. They succeeded over the course of several years to dramatically reduce the population of these small fur-bearing animals. To this day it is rare to see these animals. Ogden noted in his journal on February 14, 1827: "I have named this river Sastise River. There is a mountain equal in height to Mount Hood or Vancouver; I have named Mt. Sastise. I have given these names, from the tribes of the Indians." However historians believe he saw the Rogue River and Mount McLoughlin. Early maps portrayed today's Mount Shasta variously as Mount Pitt, Mount Jackson, and Mount Simpson and said that it was over 20,000 feet above sea level. For the most part, the explorers and fur trappers traveled through the area but did not stay for any length of time.

Early maps portrayed today's Mount Shasta variously as Mount Pitt, Mount Jackson, and Mount Simpson and said that it was over 20,000 feet above sea level. For the most part, the explorers and fur trappers traveled through the area but did not stay for any length of time. -- Mount Shasta Chamber of Commerce Website, 2002

1827

Peter Skene Ogden left Fort Vancouver and journeyed through central Oregon, trapping beaver. The trappers wanted fur from beaver, otter, and martins to export to England. They succeeded over the course of several years to dramatically reduce the population of these small fur-bearing animals. To this day it is rare to see these animals. Ogden noted in his journal on February 14, 1827: "I have named this river Sastise River. There is a mountain equal in height to Mount Hood or Vancouver; I have named Mt. Sastise. I have given these names, from the tribes of the Indians." However historians believe he saw the Rogue River and Mount McLoughlin. -- Mount Shasta Chamber of Commerce Website, 2002

1854

In August of 1854, a party of eight made the first attempt to reach the summit of the celebrated Shasta Butte, or Mount Shasta, then thought to be the highest peak in California. Mr. E.D. Pierce, a Yreka local man led the group. They raised the United States flag on the summit amid loud cheers from the small party. A narrative of the adventure was published in the San Francisco Daily Herald, but many were doubtful of its truth, so about a month later another group of nine men led by Mr. Pierce again made for the lofty summit. This time they etched their names on a rock at the summit. They explored the vent of the hot spring where several men became nauseated from inhaling the sulfuric gases. They estimated the distance to the summit to be seven miles and the elevation to be between twelve to sixteen thousand feet above sea level. -- Mount Shasta Chamber of Commerce Website, 2002

1976

December 1976, Mount Shasta desigated National Natural Landmark. -- U.S. National Park Service Website, 2003

Mount Shasta: Siskiyou County - 60 miles north of Redding. One of the world's largest and most impressive stratovolcanoes containing five glaciers and consisting of four distinct but overlapping cones. Second highest of the 15 main volcanoes in the Cascade Range; only Mount Rainier is higher. Owner: Federal. Designation Date: December 1976.

Mount Shasta, a compound stratovolcano rising 3,500 meters above its base to an elevation of 4,317 meters, dominates the landscape of northern California. The largest stratovolcano of the Cascade chain at approximately 350 cubic kilometers, it compares in volume to such well know massive stratovolcanoes as Fuji-san (Japan) and Cotopaxi (Ecuador). Mount Shasta hosts five glaciers, including the Whitney Glacier, the largest in California. ... Shastina is a large subsidiary cone that rises to 3,758 meters on the west flank of the compound volcano.

Four major cone-building episodes built most of the stratovolcano around separate central vents. The main bulk of the cones built in each of these episodes appears to have accumulated in a short time, lasting perhaps only a few hundred or a few thousand years, during which numerous lavas erupted, mainly from the central vent; the final major eruptions from each of the central craters produced dacitic domes and dense-fragment pyroclastic flows. After each episode of rapid cone building, the volcano underwent significant erosion while less frequent eruptions occurred, both from the central vent and from numerous flank vents. The flank eruptions typically produced cinder cones, small monogenetic lava cones, or domes, the latter commonly accompanied by pyroclastic flows. Pyroclastic flows are particularly conspicuous on the west flank of Shastina and its major flank vent, Black Butte.

The Mount Shasta magmatic system has evolved more or less continuously for at least 590,000 years, but the ancestral cone was virtually destroyed by an enormous volcanic sector avalanche and landslide around 300,000 years ago. Only a small remnant of this older edifice remains on the west side of the stratovolcano. Shasta Valley to the north is largely floored by the debris of the sector collapse, likely representing a considerable fraction of the volume of the ancestral cone. The Sargents Ridge cone, oldest of the four major edifices that formed the present compound volcano after the major sector collapse, is younger than approximately 250,000 years, has undergone two major glaciations, and is exposed mainly on the south side of Mount Shasta. The next younger Misery Hill cone is younger than approximately 130,000 years, has been sculpted in one major glaciation, and forms much of the upper part of the mountain. The two younger cones are Holocene. Shastina, west of the cluster of other central vents, was formed mainly between 9,700 and 9,400 years; the Hotlum cone, which forms the summit and the north and northwest slopes of Shasta, may overlap Shastina in age, but most of the Hotlum cone is probably younger. Mount Shasta has continued to erupt at least once every 600-800 years for the past 10,000 years. Its most recent eruption probably was in 1786. Evidence for this eruption, recorded from sea by the explorer La Perouse, is somewhat ambiguous, but his description could only have referred to Mount Shasta. A small craterlike depression in the summit dome, containing several small groups of fumaroles and an acidic hot spring, might have formed during that eruption; lithic ash preserved on the slopes of the volcano and widely to the east yields charcoal dates of about 200 years. ...

Mount Shasta Area:

Lava Flows: Many lava flows and one cinder cone erupted at several vents between 10,000 and about 2,000 years ago.

Domes: Two domes formed between about 10,000 and 9,000 years ago; one formed during the last approximately 2,000 years.

Tephra: Two tephra eruptions of small volume occurred between approximately 10,000 and 9,000 years ago; probable volume 0.001-0.1 cubic kilometers.

Pyroclastic Flows: Many pyroclastic flows down all sides of the volcano; some traveled 20 kilometers or more from the summit.

Debris Flows: Many debris flows down all sides of the volcano; many reached more than 30 kilometers from the volcano; one reached more than 40 kilometers from the volcano.

Most recent eruption: Small pyroclastic flows, associated ash clouds and debris flows about 200 carbon-14 years ago.

Most probable future potential hazard: Formation of large pyroclastic flows and debris flows.

Modern Mount Shasta is made up of at least four overlapping cones, the oldest of which is more than 100,000 years old and froms the south flank of the Volcano. Even this oldest cone, however, probably postdates the debris-avalanche deposits in Shasta Valley and may itself represent more than one "evolutionary cycle" in the growth of Mount Shasta. Volcanic rocks that evidently are older than this cone, and that predate the debris avalanche, crop out at the west base of the volcano. ...

The debris-avalanche deposits underlie the western two-thirds of Shasta Valley, which is a broad depression between the Klamath Mountains on the west and the Cascade Range on the east. The valley is drained by the Shasta River, which flows northward across the avalanche deposits and younger basaltic lava flows. The river enters a bedrock gorge in the Klamath Mountains northwest of Montague and joins the Klamath River about 10 kilometers farther downstream. The floor of the southern part of Shasta Valley slopes northward from an altitude of a little over 900 meters near Weed to about 760 meters near Montague, and part of the valley that lies north of Montague slopes gently southward. Mount Shasta volcano, which has a summit altitude of 4,316 meters and an estimated volume of about 335 cubic kilometers, lies at the south end of the valley. ...

Volcanic rocks of Tertiary age border the north and east sides of Shasta Valley and also form a few hills that rise above the central part of the valley floor, such as Steamboat Mountain and Owls Head. Gregory Mountain at Montague is a cylindrical neck or plug of hornblende andesite. ...

Mount Shasta Eruptive History - Menu

The deposits of an exceptionally large debris avalanche extend from the base of Mount Shasta volcano northward across the floor of Shasta Valley in northern California. The debris-avalanche deposits underlie an area of about 675 square kilometers, and their estimated volume is at least 45 cubic kilometers. Radiometric limiting dates suggest that the debris avalanche occurred between about 300,000 and 380,000 years ago. Hundreds of mounds, hills, and ridges formed by the avalanche deposits are separated by flat areas that slope generally northward at about 5 meters per kilometer. The hills and ridges are formed by the block facies of the deposits, which includes masses of andesite lava tens to hundreds of meters across as well as stratigraphic successions of unconsolidated deposits of pyroclastic flows, lahars, air-fall tephra, and alluvium, which were carried intact within the debris avalanche. The northern terminus of the block facies is near Montague, at a distance of about 49 kilometers from the present summit of the volcano. The flat areas between hills and ridges are underlain by the matrix facies, which is an unsorted and unstratified mudflowlike deposit of sand, silt, clay, and rock fragments derived chiefly from the volcano. Boulders of volcanic rock from Mount Shasta are scattered along the west side of Shasta Valley and in the part of Shasta Valley that lies north of Montague, at heights of as much as 100 meters above the adjacent surface of the debris-avalanche deposits. The boulders represent a lag that was formed after the main body of the avalanche came to rest, when much of the still-fluid matrix facies drained away and flowed out of Shasta Valley down the Shasta River valley and into the Klamath River.

The debris avalanche probably originated in a quick succession of huge landslides of water-saturated rock on the northwest flank of ancestral Mount Shasta, each of which cut progressively deeper into the volcano. Evidence is lacking of contemporaneous volcanic activity, and the cause of the landslides is not known.

Mount Shasta Debris Avalanche - Menu

Mount Shasta hosts five glaciers, including the Whitney Glacier, the largest in California.

Mount Shasta Glaciers - Menu

Streams that head on Mount Shasta enter three main river systems: the Shasta River to the northwest, the Sacramento River to the west and southwest, and the McCloud River to the east, southeast, and south. Creeks draining the northeast flank of Mount Shasta flow into a closed depression in which fans of debris from Mount Shasta abut the pre-Shasta lava cones of The Whaleback and Ash Creek Butte. Many streams draining Mount Shasta are intermittent and disappear into coarse fan debris at the base of the volcano.

Between 1980 and 1984, the U. S. Geological Survey's David A. Johnston Cascades Volcano Observatory (CVO) established baseline geodetic networks at Mount Baker, Mount Rainer, and Mount St. Helens in Washington, Mount Hood and Crater Lake in Oregon, and Mount Shasta and Lassen Peak in California. To this list of potentially active volcanoes, CVO extended its monitoring program in 1985 to include Newberry and South Sister volcanoes in central Oregon. The Newberry and South Sister networks were re-measured in 1986 and will be measured periodically in future years. Improvements since 1984 in the recording of endpoint and flightline temperatures resulted in better overall data than obtained previously. The improvements included: calibration of all the sensors and precision thermistors, installation of a new recording system for flightline data, and recording of endpoint temperatures 6 meters above ground level. The data collected in 1985 and 1986 indicate little or no apparent deformation at either volcano between surveys.

Mount Shasta Monitoring Menu

Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years. Holocene eruptions also occurred at Black Butte, a group of overlapping dacite domes about 13 kilometers west of Mount Shasta. (Christiansen and Miller, 1976; Miller, 1978). ... The extrusion of the domes about 9,500 years ago was accompanied by the formation of pyroclastic flows which extended more than 10 kilometers south and 5 kilometers north of the domes. ...

Pyroclastic flows have been formed frequently at Mount Shasta during the last 10,000 years; they have flowed down most sides of the mountain and have traveled as far as 20 kilometers from their sources. Future pyroclastic flows from vents or domes near the summit could sweep down almost any side of the mountain, although the area west of Shastina would probably be protected by the barrier formed by the Shastina cone. If future eruptions were to occur at new vents or domes located on a flank of the volcano, pyroclastic flows would primarily affect only those areas of the mountain downslope from the vents. ... Pyroclastic flows from vents low on the flank of, or near, Mount Shasta might spread more radially and travel in several directions from the source. Such an event occurred at Black Butte about 9,500 Carbon14 years ago, when pyroclastic flows produced by collapse or explosion of dome segments of Black Butte traveled about 10 kilometers south and 5 kilometers north of the dome complex and covered an area of about 45 square kilometers (Miller, 1978).

Mount Shasta, a compound stratovolcano rising 3,500 meters above its base to an elevation of 4,317 meters, dominates the landscape of northern California. ... Shastina is a large subsidiary cone that rises to 3,758 meters on the west flank of the compound volcano.

Four major cone-building episodes built most of the stratovolcano around separate central vents. The main bulk of the cones built in each of these episodes appears to have accumulated in a short time, lasting perhaps only a few hundred or a few thousand years, during which numerous lavas erupted, mainly from the central vent; the final major eruptions from each of the central craters produced dacitic domes and dense-fragment pyroclastic flows. After each episode of rapid cone building, the volcano underwent significant erosion while less frequent eruptions occurred, both from the central vent and from numerous flank vents. The flank eruptions typically produced cinder cones, small monogenetic lava cones, or domes, the latter commonly accompanied by pyroclastic flows. Pyroclastic flows are particularly conspicuous on the west flank of Shastina and its major flank vent, Black Butte.

Black Butte Menu

Mount Shasta, a compound stratovolcano rising 3,500 meters above its base to an elevation of 4,317 meters, dominates the landscape of northern California. ... Shastina is a large subsidiary cone that rises to 3,758 meters on the west flank of the compound volcano. ...

Shastina, west of the cluster of other central vents, was formed mainly between 9,700 and 9,400 years; the Hotlum cone, which forms the summit and the north and northwest slopes of Shasta, may overlap Shastina in age, but most of the Hotlum cone is probably younger.

Mount Shasta is located in the Cascade Range in northern California about 65 kilometers (40 miles) south of the Oregon-California border and about midway between the Pacific Coast and the Nevada border. One of the largest and highest of the Cascade volcanoes, snowclad Mount Shasta is near the southern end of the range that terminates near Lassen Peak. Mount Shasta is a massive compound stratovolcano composed of overlapping cones centered at four or more main vents; it was constructed during a period of more than 100,000 years. ... Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years.

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